THE EFFECT OF COAL TYPE IN DRY-SORBENT/COAL INJECTION FOR CONTROL OF SO_2 AND NO_x EMISSIONS

摘要

Simultaneous reduction of NO_x, SO_2 and particulate emissions from powerplants is achieved by a method combining injection of sorbent/coal blends with a ceramic honeycomb filter. The filter is mounted in an elevated temperature region where it retains sorbent particles for prolonged periods of time and facilitates their utilization until it is eventually regenerated (cleaned). The filter also captures and oxidizes particulate carbon, which otherwise might contribute to the formation of air toxics, such as dioxins, as the effluent cools further. The performance of commercial sorbents, such as calcium carbonate [CaCO_3] and sodium bicarbonate [NaHCO_3], as well as the porous sorbent calcium formate [Ca(COOH)_2] was evaluated in the laboratory. The sorbent powders were blended with three types of pulverized coal to achieve NO_x reduction, i.e., bituminous, sub-bituminous and lignite. The sorbents/coal blends were injected in a simulated effluent gas containing SO_2 and NO at a gas temperature of 1150°C (1423 K), upstream of a ceramic filter, which was kept at 600°C (873K). The molar Ca/S ratio was in the neighborhood of 2, and the fuel-to-air equivalence ratio, Φ, was also in the neighborhood of 2 (fuel-rich) for all tests. In this work, emphasis is placed on differentiating the effects of the aforementioned coal types on reducing both the SO_2 and the NO_x emission concentrations. Results show that SO_2 removal efficiencies in the range of 35-80% were achieved, depending on the coal and the sorbent used. NO_x reduction efficiencies of 45-55% were obtained, depending on the coal. Particulate removal efficiencies by the filter have been measured to be in the range of 97-99%.